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SubjectRe: [patch] revert: [NET]: Fix races in net_rx_action vs netpoll
Hi,

Here is my proposal of a solution based on dev->state flag,
but intended mainly to prevent poll_napi from disturbing
while net_rx_action is running and polling the device.

It doesn't look very nice or clean but I hope it could
guard net_rx_action enough with some room for netpoll too.

I'd be very glad if it could be verified and/or tested.

Regards,
Jarek P.

PS: not tested!

---

diff -Nurp 2.6.22-git9-/include/linux/netdevice.h 2.6.22-git9/include/linux/netdevice.h
--- 2.6.22-git9-/include/linux/netdevice.h 2007-07-18 07:50:56.000000000 +0200
+++ 2.6.22-git9/include/linux/netdevice.h 2007-07-18 13:21:12.000000000 +0200
@@ -262,6 +262,8 @@ enum netdev_state_t
__LINK_STATE_LINKWATCH_PENDING,
__LINK_STATE_DORMANT,
__LINK_STATE_QDISC_RUNNING,
+ /* Set by net_rx_action vs poll_napi */
+ __LINK_STATE_POLL_LIST_FROZEN,
};


diff -Nurp 2.6.22-git9-/net/core/dev.c 2.6.22-git9/net/core/dev.c
--- 2.6.22-git9-/net/core/dev.c 2007-07-18 07:50:58.000000000 +0200
+++ 2.6.22-git9/net/core/dev.c 2007-07-18 13:18:23.000000000 +0200
@@ -2025,6 +2025,7 @@ static void net_rx_action(struct softirq
unsigned long start_time = jiffies;
int budget = netdev_budget;
void *have;
+ struct net_device *dev_frozen = NULL;

local_irq_disable();

@@ -2040,15 +2041,35 @@ static void net_rx_action(struct softirq
struct net_device, poll_list);
have = netpoll_poll_lock(dev);

+#ifdef CONFIG_NETPOLL
+ /* prevent a race with poll_napi() */
+ if (dev_frozen && dev_frozen != dev) {
+ clear_bit(__LINK_STATE_POLL_LIST_FROZEN,
+ &dev_frozen->state);
+ set_bit(__LINK_STATE_POLL_LIST_FROZEN,
+ &dev->state);
+ dev_frozen = dev;
+ } else if (!dev_frozen) {
+ set_bit(__LINK_STATE_POLL_LIST_FROZEN,
+ &dev->state);
+ dev_frozen = dev;
+ }
+#endif
if (dev->quota <= 0 || dev->poll(dev, &budget)) {
netpoll_poll_unlock(have);
local_irq_disable();
- list_move_tail(&dev->poll_list, &queue->poll_list);
+ list_move_tail(&dev->poll_list,
+ &queue->poll_list);
if (dev->quota < 0)
dev->quota += dev->weight;
else
dev->quota = dev->weight;
} else {
+#ifdef CONFIG_NETPOLL
+ clear_bit(__LINK_STATE_POLL_LIST_FROZEN,
+ &dev->state);
+ dev_frozen = NULL;
+#endif
netpoll_poll_unlock(have);
dev_put(dev);
local_irq_disable();
@@ -2056,6 +2077,14 @@ static void net_rx_action(struct softirq
}
out:
local_irq_enable();
+#ifdef CONFIG_NETPOLL
+ if (dev_frozen) {
+ have = netpoll_poll_lock(dev_frozen);
+ clear_bit(__LINK_STATE_POLL_LIST_FROZEN,
+ &dev_frozen->state);
+ netpoll_poll_unlock(have);
+ }
+#endif
#ifdef CONFIG_NET_DMA
/*
* There may not be any more sk_buffs coming right now, so push
diff -Nurp 2.6.22-git9-/net/core/netpoll.c 2.6.22-git9/net/core/netpoll.c
--- 2.6.22-git9-/net/core/netpoll.c 2007-07-18 07:50:58.000000000 +0200
+++ 2.6.22-git9/net/core/netpoll.c 2007-07-18 12:09:43.000000000 +0200
@@ -124,13 +124,20 @@ static void poll_napi(struct netpoll *np
if (test_bit(__LINK_STATE_RX_SCHED, &np->dev->state) &&
npinfo->poll_owner != smp_processor_id() &&
spin_trylock(&npinfo->poll_lock)) {
- npinfo->rx_flags |= NETPOLL_RX_DROP;
- atomic_inc(&trapped);
+ /*
+ * If POLL_LIST_FROZEN is set net_rx_action
+ * is working with this device.
+ */
+ if (!test_bit(__LINK_STATE_POLL_LIST_FROZEN,
+ &np->dev->state)) {
+ npinfo->rx_flags |= NETPOLL_RX_DROP;
+ atomic_inc(&trapped);

- np->dev->poll(np->dev, &budget);
+ np->dev->poll(np->dev, &budget);

- atomic_dec(&trapped);
- npinfo->rx_flags &= ~NETPOLL_RX_DROP;
+ atomic_dec(&trapped);
+ npinfo->rx_flags &= ~NETPOLL_RX_DROP;
+ }
spin_unlock(&npinfo->poll_lock);
}
}
-
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